FIG. 2 shows a cross-sectional view of a prior art planar type quantum well laser utilizing p type impurity diffusion described in Prescript No. 18a-ZR-9 of 1987 Autumn Meeting of Japanese Society of Applied Physics.
In FIG. 2, reference numeral 1 designates a semi-insulating GaAs substrate. A P type AlGaAs lower cladding layer 2 is disposed on GaAs substrate 1. A Multi-quantum well (hereinafter referred to as MQW) layer 3, the active layer is disposed on the p type AlGaAs lower cladding layer 2. An n type AlGaAs upper cladding layer 4 is disposed on MQW layer 3. An n type GaAs contact layer 5 is disposed on the n type AlGaAs upper cladding layer 4. Reference numeral 6 designates Zn diffusion regions. P side electrodes 7 are disposed on the Zn diffusion regions 6. An n side electrode 8 is disposed on the n type GaAs contact layer 5. Reference numeral 30 designates an MQW layer disordered by Zn diffusion.
The production process will be described.
First of all, a p type AlGaAs layer 2, an MQW layer 3 an n type AlGaAs layer 4, and an n type GaAs contact layer 5 are successively grown on a semi-insulating GaAs substrate 1. There after, zinc is selectively diffused into the structure, leaving the MQW layer 3 in a stripe configuration. Thereafter, the pn junction portion of the contact layer 5 is etched and removed, and a p and an n side electrode 7 and 8 are deposited, thereby completing a semiconductor laser.
The operation will be described.
The MQW 30 in the zinc diffused region 6 is disordered so that the AlGaAs has a larger band gap than that of the well layer of the MQW. A current flowing into the device from the p side electrode 7 is injected into the MQW layer 3 which is not disordered, thereby to generate light. The diffusion voltage of the MQW layer 3 is lower than that of the upper and lower AlGaAs layers 2 and 4. By narrowing the width of the light emission region sufficiently, a stable single mode oscillation is obtained and a low threshold current is obtained. Further, in this structure, both the p and n side electrodes are disposed on the same surface of the device and the therebetween is small enough for use in an integrated circuit.
The prior art planar type p diffusion quantum well laser is produced as described above. When the light emission region width is narrowed, the production of the n side electrode becomes difficult, limiting the reduction of the threshold current.